A television signal may include auxiliary information in addition to video program and audio program information. For example, an NTSC (National Television Standards Committee) television signal may include two bytes of closed captioning data during the latter half of each occurrence of line 21 of field 1. Closed caption data may be decoded and displayed to provide a visible text representation of a television programs audio content. Additional closed caption data and other types of auxiliary information, such as extended data services information (XDS), may be included in other line intervals such as line 21 of field 2. These other types of auxiliary data such as XDS are encoded in a similar manner to closed caption data and can be decoded using a caption decoder. Because most television receivers sold in the U.S. include caption decoders (U.S. law requires all television receivers larger than 13 in size to include a caption decoder), most television receivers can decode and utilize auxiliary data such as XDS data.
One important application of XDS data is providing the so-called V-chip capability. A television receiver that provides V-chip capability permits a user to prevent certain programs and/or scenes from being viewed and heard based on the content of the program/scenes. For example, a user might specify that programs and/or scenes including violent subject matter should be excluded. Alternatively, a user can specify a rating limit, such as PG-13, and programs and scenes exceeding that limit (e.g., R and X rated programs) could not be viewed or heard. By decoding program content information included in XDS data, a television receiver can determine the content and rating of television programs and scenes and can compare the content and rating to the limits set by a user. For those programs and scenes that exceed the specified limits, the video display is modified, e.g., blanked, and the audio is muted. In addition, the receiver may display a message indicating the reason for the interrupted reception and the expected duration of the interruption (e.g., SCENE EXCEEDS CONTENT LIMIT).
In addition to auxiliary data decoding capability, certain television receivers also include multi-image display capability. For example, certain television receivers include a picture-in-picture ("pix-in-pix" or "PIP") feature that, when activated, produces an image signal representing both a main image region and an auxiliary image region. A displayed image produced in response to the signal includes the auxiliary image (also referred to as "PIP image" or "small image) inset into the main image. Typically, the auxiliary image region displays video from a video source other than that supplying the main image region. For example, an auxiliary video signal source such as a VCR or a second tuner may provide the auxiliary video signal.